fix(python): Raise suitable error when invalid column passed to get_column_index

[alexander-beedie]

Invalid column name lookups were returning None from get_column_index.

This isn't consistent with get_column or the function typing (which indicates it will only return int, or raise an error), and was discovered after tracking down a much more cryptic error at work caused by the unexpected None :)

Now raises the expected ColumnNotFoundError.
Test coverage added.

Example

df = pl.DataFrame({
  "foo": [1, 2, 3],
  "bar": [4, 5, 6],
  "ham": [7, 8, 9],
})

Column exists; returns index:

df.get_column_index("ham")
# 2

Column does not exist; raises the expected error:

df.get_column_index("sandwich")
# ColumnNotFoundError: sandwich

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.48%. Comparing base (3016c07) to head (a77f7e5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17868      +/-   ##
==========================================
+ Coverage   80.47%   80.48%   +0.01%     
==========================================
  Files        1505     1505              
  Lines      197273   197276       +3     
  Branches     2807     2808       +1     
==========================================
+ Hits       158764   158787      +23     
+ Misses      37987    37967      -20     
  Partials      522      522              

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[stinodego]

Thanks! We should just point to try_get_column_index. See comments!

[alexander-beedie]

Thanks! We should just point to try_get_column_index. See comments!

Yup; done ;)